State-of-the-art power supplies in general-purpose computers typically use pulse-width modulation to digitally regulate power generation. A typical power supply first converts the incoming 60-Hz utility power frequency to a much higher frequency range, such as 20,000 cycles per second. The duration of each power pulse is varied in response to the needs of the computer circuitry being supplied. The width of the pulses is controlled by electronically switching the current flow on and off. The pulses are reduced in voltage by a step-down transformer and turned into direct current by rectification and filtering. Switching the current off and on reduces losses in power from heat dissipation and makes power supplies relatively efficient.
Power supplies used by general-purpose computers produce different distinct voltages that are used by powered devices and circuits within each machine. Nearly all circuitry in state-of-the-art computers, from microprocessors to memory, requires either 5 or 3.3 volts. The motors of most disk drives use either 12 or 5 volts. Serial ports and some other input/output (I/O) devices often require both a positive and negative 12 volt supply. A few components and peripherals also require a negative 5 volt direct current supply.
Typically, a single power supply supplies all required voltages and varying amperage requirements to the different components that comprise a general-purpose computer system. The power supply's maximum power output must be rated close to the sum of all the power needs of installed components and expected addition of peripherals. It is a common practice, therefore, to provide a power supply rated considerably higher than the average usage of a system.
To work at optimum efficiency, the ratio of minimum to maximum load, or minimum to maximum power requirement, should not exceed a ratio of approximately 1:6. When a much larger power supply than is needed is initially installed, power efficiency is decreased for low power modes of operation. Efficiency may also be affected negatively when personal general-purpose computers incorporate advanced power (APM) management systems that have low-power modes, such as a standby mode.
Typically, these power-saving computers have four operating modes, with greatly varying power consumption. As an example, power modes in a typical portable general purpose computer may be as follows: a peak mode at approximately 90 watts for power-on surge; a normal mode at about 50 watts for operation with full expansion capabilities; a suspend mode at about 10-15 watts for no processing activity, but data is retained in random access memory (RAM); and a standby mode at about 1-2 watts for power only to wake-up circuits. Control for these power management modes is typically incorporated into the basic input/output system (BIOS) and works independently of state-of-the-art installed power supplies.
In this example, a power-saving system consumes as little as 1-2 watts in standby mode and as much as 90 watts in the power-on peak mode as described above. This design reduces power efficiency in trade for a power management system with low-power standby modes. In an additional effort to save power, manufacturers of general-purpose computers are reducing voltage levels to 3.3 volts for system microprocessors, integrated circuits and memory. This decreases power efficiency further when only system board functions are activated.
Designing and producing power-saving computers can significantly reduce the use of valuable natural resources. The Environmental Protection Agency (EPA) estimates that the annual energy consumption of office equipment has risen 400 percent between 1983 and 1993, and computers represent a large portion of this growth. That is a compound annual growth rate of about 17 percent, exceeding most estimates of workplace productivity improvements for the same period. Considering very low efficiencies associated with electric air-conditioning required to cool computerized equipment, every watt that goes into a general-use computer may actually represents as much as 3.3 watts of total demand. It is estimated by the EPA that the power to operate a personal computer and cool the space around it may cost as much as a personal computer costs on an annualized depreciation basis. These considerations have prompted the EPA to establish an Energy Star Computer Program to affix a government Energy Star seal on desk-top and workstation computers that can maintain a suspend mode of less than 30 watts. The federal government has even expressed that in the future they will but only such machines.
What is needed now is a power supply system for general-purpose computers that can be efficient at low power modes but can still have sufficient peak power for expanded configurations, with even larger power demands at varying time intervals. The present invention optimizes the use of an APM system with a power supply that can deliver optimized efficiency over different load requirements.